Method and device for the detection of surface defects on the finish of a transparent or translucent rotating container

ABSTRACT

A device for detecting surface defects ( 2 ) on the neck ring ( 3 ) of a container comprises: 
         a light source ( 5 ) illuminating, by means of an incident light beam, a section of the surface of the neck ring of the container, along a determined incident direction (D i ),    at least one linear sensor ( 10 ) measuring light beams, arranged to receive the light beam reflected by the surface defect, the angle (α) between the incident (D i ) and reflection (D r ) directions lying between 15 and 45°, preferably in the order of 30°, one of the directions being parallel to the axis of revolution of the container,    means ( 15 ) for ensuring the rotation of the container about the axis of revolution through at least one rotation,    and a unit ( 16 ) for analysing and processing light beams received by the linear sensor, to identify the presence of a surface defect.

The present invention concerns the technical area of inspecting objects,hollow items or, generally any transparent or translucent containerssuch as glass bottles, flasks or jars.

The subject of the invention more precisely concerns the inspection ofsuch containers to detect the presence of surface defects on the neckring of said containers, such as a material defect, called line defectcorresponding to excess or shortage of material (line over finish),defects called seeds or blisters, or defects corresponding to a chippedring.

The state of the art proposes various devices for inspecting the qualityof container neck rings so as to eliminate those carrying defects whichmay detract from their appearance or, more seriously, constitute a truehazard for users. For example, a detection device is known throughdocuments EP 0 497 477 or JP 10 062 359, comprising a light source ableto provide an incident beam concentrated on the upper surface of theneck ring. A camera is positioned so as to receive the reflected lightbeams which are transmitted to a processing unit, adapted tore-constitute an image of the ring surface after rotating the object ona lathe. The processing unit analyses variations of the image in timeand space to detect the presence of any defects. Said technical solutiondoes not give satisfaction in practice, insofar as the images sufferfrom extensive stray light due to the different light reflections on thesurface of the container. Surface irregularities of the neck ringgenerate extensive noise and mask minor defects such as line defects.

The purpose of the invention is to overcome the afore-mentioneddrawbacks by putting forward a reliable detection solution to detect, onthe neck ring of a transparent or translucent container having an axisof revolution, any surface defects that are generally difficult todetect such as line defects.

To attain this objective, the subject of the invention sets out topropose a method to detect surface defects on the neck ring of atransparent or translucent container having an axis of revolution, whichcomprises the following steps:

-   -   illuminating a section of the neck ring surface of the container        with an incident light beam, along a determined incident        direction,    -   arranging a linear measuring sensor along a determined direction        of reflection, to collect the light beam reflected by the        surface defect on the neck ring, the angle between the incident        and reflection directions lying between 15 and 45°, preferably        in the order of 30°, one of the directions being parallel to the        axis of revolution of the container,    -   ensuring rotation of the container about the axis of revolution        through at least one revolution,    -   and processing the light beams received by the linear sensor so        as to create and analyse an image to identify the presence of        any surface defect corresponding to a bright area.

According to a preferred characteristic of embodiment, the methodconsists of using an incident light beam to illuminate a radial sectionof the neck ring surface of the container.

According to this preferred variant of embodiment, one of the directionsof reflection or incidence is parallel to the axis of revolution of thecontainer, whilst the other direction extends along a planeperpendicular to the radial plane of the container and parallel to theaxis of revolution.

According to one advantageous characteristic of embodiment, the methodconsists of analysing the image by conducting an analysis of the formcharacteristics of the bright areas, so as to identify the presence of asurface defect.

According to another advantageous characteristic of embodiment, themethod consists of using an incident light beam to illuminate a radialsection of the neck ring surface of a container along a determinedincident direction, parallel to the axis of revolution of the container,and of arranging a linear measuring sensor parallel to the radial planeand oriented along a direction extending in a plane perpendicular to theradial plane and parallel to the axis of revolution.

According to this advantageous characteristic of embodiment, the methodconsists of arranging a second linear measuring sensor symmetrical tothe first linear measuring sensor with respect to the radial plane.

A further subject of the invention is to propose a device for detectingsurface defects on the neck ring of a transparent or translucentcontainer having an axis of revolution, the device comprising:

-   -   a light source adapted to illuminate, with an incident light        beam, a section of the neck ring surface of the container, along        a determined incident direction,    -   at least one linear sensor for measuring the light beam,        arranged to receive the light beam reflected by the surface        defect of the neck ring, the angle between the incident and        reflection directions lying between 15 and 45°, preferably in        the order of 30°, one of the directions being parallel to the        axis of revolution of the container,    -   means ensuring rotation of the container about the axis of        revolution through at least one revolution,    -   and an analysis and processing unit for the light beams received        by the linear sensor and adapted to create an image and analysis        the image, so as to identify the presence of a surface defect        corresponding to a bright area.

According to a preferred characteristic of embodiment, the light sourceilluminates a radial section of the neck ring surface of the containerwith an incident light beam.

Advantageously, the light source and the linear measuring sensor arepositioned so that either one of the reflection or incident directionsis parallel to the axis of revolution of the container, whilst the otherdirection extends along a plane perpendicular to the radial plane of thecontainer and parallel to the axis of revolution.

According to a preferred characteristic of embodiment, the analysis andprocessing unit comprises means for analysing the form characteristicsof the bright areas so as to identify the presence of a surface defect.

According to a preferred variant of embodiment, the light sourceilluminates a radial section of the ring surface of the container withan incident light beam, the linear measuring sensor being positionedparallel to the radial plane and being oriented along a directionextending in a plane perpendicular to the radial plane and parallel tothe axis of revolution.

Advantageously, the device of the invention comprises a second linearmeasuring sensor, positioned symmetrically to the first linear measuringsensor with respect to the radial plane.

Various other characteristics will become apparent from the descriptiongiven below with reference to the appended drawings which shownon-restrictive examples of embodiments of the subject of the invention.

FIG. 1 is a schematic elevation view illustrating the implementation ofa detection device according to the invention.

FIGS. 2 a and 2 b are perspective views illustrating the operatingprinciple of the detection device of the invention.

FIG. 3 is a schematic, showing a cross-section view of a container,illustrating the projection of light beams by the detection device ofthe invention.

FIG. 4 is a picture taken by a detection device of the invention.

As emerges more precisely from FIGS. 1 to 3, the subject of theinvention concerns a method and a device 1, adapted to detect defects onthe surface 2 of a neck ring 3 of a transparent or translucent container4 having an axis of revolution or symmetry X. Said device 1 comprises alight source 5 adapted to illuminate, via an incident light beam 6, asection s of surface 2 of the container neck ring along a determinedincident direction D_(i).

According to a preferred characteristic of embodiment, the light source5 via an incident light beam 6, illuminates a radial section s ofsurface 2 of the container neck ring, as can be seen precisely in FIG.3. The radial section s of surface 2 of the neck ring therefore relatesto the thickness of a wall of container 4 at the surface 2 of the neckring and in a plane passing through the axis of revolution X. In theexample of embodiment illustrated in the drawings, the light source 5 ispositioned so as to illunmiate, via its incident light beam 6, a radialsection s of surface 2 of the neck ring 3 of container 4, along adetermined incident direction D_(i) parallel to the axis of revolution Xof the container (FIG. 2 b).

Device 1 of the invention also comprises at least one linear sensor 10for measuring light beams, arranged to receive the light beams 11reflected by defects on the surface 2 of neck ring 3 of the container.The linear measuring sensor 10, such as a camera, is positioned tocollect the light beams 11 reflected by section s of surface 2 of theneck ring. In this respect, the line of photosensitive cells of camera10 is oreinted along a direction parallel to section s of surface 2illuminated by the incident beam 6. In the preferred example ofembodiment, for which the light source 5 illuminates a radial section sof the neck ring of the container, the linear measuring sensor 10 ispositioned parallel to the radial plane R.

Also, the sighting axis of the camera 10, schematised by the reflectedlight beam 11, therefore extends along a direction of reflection D_(r)which, with the incident direction D_(i), forms an angle α of between 15and 45° preferably in the order of 30°. In the preferred example ofembodiment illustrated in the drawings and in which the light source 5illuminates a radial section s of the neck ring, camera 10 is orientedalong a direction of reflection D_(r) in a plane P perpendicular to theradial plane R and parallel to the axis of revolution X (FIG. 2 b).Evidently, this plane P, along which the sighting axis of camera 10extends, cuts the radial section s of the ring illuminated by theincident light beam 6, so that the line of photosensitive cells is ableto scan section s of surface 2 of the neck ring, over a given elementarywidth.

In the illustrated example, it is to be noted that the incidentdirection D_(i) of the light beam is parallel to the axis of revolutionX of the container. Evidently, the position between the light source 5and the linear measuring sensor 10 may be interchanged. According tothis variant of embodiment, the direction of reflection D_(r), in whichcamera 10 is positioned, is parallel to the axis of revolution X of thecontainer, while the incident direction D_(i) of the incident light beam6 is inclined so that, with the direction of reflection D_(r), it formsangle α previously defined.

The relative positioning of light source 5 and the linear measuringsensor 10, makes it possible to recover only the light reflected by thedefects on surface 2 of the neck ring 3. The linear measuring sensor 10is positioned so as not to receive the light reflected by the ringsurface not having any defects. In the example of embodiment illustratedin the drawings, the incident light 6, parallel to the axis ofrevolution X of the container, is transmitted or reflected along thesame axis when ring surface 2 does not have any defects. Therefore, onlypart of the light reflected by the defects of surface 2 at angle α isdetected by the camera 10. In this manner, the surface defects are notmasked by the direct reflection of surface 2. Said method of detectionprovides reliable, efficient detection even for minor surface defects.

The detection device 1 of the invention also comprises means 15 ensuringthe rotation of the container 4 about its axis of revolution X throughat least one complete rotation so that the camera scans the entirety ofsurface 2 of the neck ring 3 of container 4. Rotation of the container 4about its axis of revolution X enables the camera to successivelyvisualize each of section s of elementary width which together form thesurface 2 of neck ring 3.

Detection device 1 of the invention also comprises an analysis andprocessing unit 16 connected to the linear measuring sensor 10. Thisunit 16 for analysing and processing the light beams received by thelinear sensor 10 is adapted to create an image and analyse the image soas to identify, within the image, the presence of any surface defectcorresponding to a bright area. As explained above, the linear sensor 10is positioned so as to remover the light flow reflected by the defect.

The input of the analysis and processing unit 16, as is usual, comprisesan acquisition circuit having an input connection to the camera whichdelivers electronic signals representing the light intensity received byeach of the camera's photosensitive cells. The acquisition circuitensures conversion of the analogue signal into a digital signal coded ina certain number of bits in accordance with a determined scale of greys.This raw image is memorized and filtered to attenuate image contrasts.The filtered image is subtracted from the raw image to removeinterference so as to obtain a final image I, such as illustrated inFIG. 4. As explained above, the defects appear in the form of a brightarea b, since it corresponds to the light reflected by the defects. Unit16 comprises image analysis means based on analysis of the formcharacteristics of bright areas b, to identify the presence of a surfacedefect. These analysis means are used to calculate characteristics suchas the position in space, surface, perimeter, centre of gravity or levelof grey of the bright areas. Said characteristics are compared withthreshold values to determine whether or not the detected bright area bcorresponds to a defect.

According to a further characteristic of the invention, it is to benoted that the detection device 1 may comprise a second linear measuringsensor, positioned symmetrically to the first linear measuring sensor 10with respect to radial plane R. In this variant, the second linearmeasuring sensor is positioned parallel to the radial plane R, beingoriented in a direction extending along the perpendicular plane P withan angle of incline α of opposite direction with respect to directionD_(i).

The invention is not limited to the examples shown and described sincevarious modifications may be made thereto without departing from thescope of the invention.

1- Method for detecting surface defects (2), on a neck ring (3), of atransparent or translucent container (4) having an axis of revolution(X), characterized in that it comprises the following steps:illuminating, by means of an incident light beam (6), a section (s) ofthe surface (2) of the neck ring (3) of the container (4), along adetermined incident direction (D_(i)), arranging a linear measuringsensor (10), along a determined direction of reflection (D_(r)), tocollect the light beam reflected by the surface defect on the neck ring,the angle (α) between the incident direction (D_(i)) and reflectiondirection (D_(r)) lying between 15 and 45°, preferably in the order of30°, one of these directions being parallel to the axis of revolution(X) of the container, ensuring rotation of the container (4) about theaxis of revolution (X) through at least one rotation, and processing thelight beam received by the linear sensor (10), so as to create an image(I) and analyse the image to identify the presence of a surface defectcorresponding to a bright area (b). 2- Method as in claim 1,characterized in that it consists of illuminating, by means of anincident light beam (6), a radial section (s) of surface (2) of thecontainer's neck ring. 3- Method as in claim 2, characterized in thatone of the reflection (D_(r)) or incident (D_(i)) directions is parallelto the axis of revolution (X) of the container while the other directionextends along a plane (P) perpendicular to the radial plane (R) of thecontainer and parallel to the axis of revolution (X). 4- Method as inclaim 1, characterized in that it consists of analysing the image (I) byconducting an analysis of the form characteristics of the bright areas(b) in order to identify the presence of a surface defect. 5- Method asin claim 1, characterized in that it consists of illuminating, by meansof an incident light beam (6), a radial section (s) of the surface (2)of the container's neck ring (4) along a determined incident directionparallel to the axis of revolution (X) of the container, and ofarranging a linear measuring sensor (10) parallel to the radial plane(R) and oriented in a direction extending along a plane (P)perpendicular to the radial plane and parallel to the axis ofrevolution. 6- Method as in claim 5, characterized in that it consistsof arranging a second linear sensor symmetrically to the first linearmeasuring sensor (10) with respect to the radial plane (R). 7- Devicefor detecting surface defects (2) on the neck ring (3) of a transparentor translucent container (4) having an axis of revolution (X),characterized in that it comprises: a light source (5) adapted toilluminate by means of an incident light beam (6), a section (s) of theneck ring surface of the container, along a determined incidentdirection (D_(i)), at least one linear measuring sensor (10) ro measurelight beams arranged to collect the light beam reflected by the surfacedefect on the neck ring, the angle (α) between the incident (D_(i)) andreflection (D_(r)) directions lying between 15 and 45°, preferably inthe order of 30°, one of ten directions being parallel to the axis ofrevolution (X) of the container, means (15) for ensuring rotation of thecontainer about the axis of revolution through at least one rotation,and a unit (16) for analysing and processing the light beams received bythe linear sensor, adapted to create an image (I) and to analyse theimage so as to identify the presence of a surface defect correspondingto a bright area (b). 8- Device as in claim 7, characterized in that thelight source (5), by means of an incident light beam (6), illuminates aradial section (s) of the surface (2) of the container's neck ring. 9-Device as in claim 8, characterized in that the light source (5) and thelinear measuring sensor (10) are positioned so that either one of thereflection (D_(r)) or incident (D_(i)) directions is parallel to theaxis of revolution (X) of the container, while the other directionextends along a plane (P) perpendicular to the radial plane (R) of thecontainer and parallel to the axis of revolution (X). 10- Device as inclaim 7, characterized in that the analysis and processing unit (16)comprises means for analysing the form characteristics of the brightareas (b) in order to identify the presence of a surface defect. 11-Device as in claim 7, characterized in that the light source (5) bymeans of an incident light beam (6), illuminates a radial section (s) ofthe surface (2) of the neck ring of the container along a determinedincident direction (D_(i)) parallel to the axis of revolution (X) of thecontainer, and in that the linear measuring sensor (10) is positionedparallel to the radial plane (R), being oriented in a directionextending along a plane (P) perpendicular to the radial plane andparallel to the axis of revolution (X). 12- Device as in claim 11,characterized in that it comprises a second linear measuring sensor (10)positioned symmetrically to the first linear measuring sensor withrespect to the radial plane (R).